1. Field of the Invention
The present invention relates to the design of computer systems. More specifically, the present invention relates to the design of a load store unit for a computer system that supports simultaneous outstanding requests to multiple targets.
2. Related Art
Recent processor designs achieve high performance by operating multiple pipelined functional units in parallel. This allows more than one computational operation to complete on a given clock cycle. In order to keep pace with such processor designs, memory systems have been modified to allow pipelining of memory accesses. This allows memory access requests to be issued before prior memory accesses return, which can greatly increase memory system throughput.
However, if a computer program changes sources of data (targets) during program execution, such pipelined memory systems typically stall, which can greatly degrade system performance. For example, if a program makes an access to a graphics co-processor in between pipelined accesses to main memory, the accesses to main memory will stall. This can be a significant problem for processor designs that support interleaved accesses to many different sources of data (targets). For example, a given processor may be able to access data from a data cache, a main memory, a graphics co-processor and from a variety of bus interfaces.
Furthermore, such pipelined memory systems typically issue at most one access request on a given clock cycle, which can limit performance in situations where multiple requests are simultaneously generated by multiple pipelined functional units, or when multiple requests have been accumulated in a buffer due to resource conflicts.
What is needed is a memory system design that overcomes these performance limitations of existing memory systems.